1. Field of the Invention
One disclosed aspect of embodiments relate to an electromechanical transducer and a method of producing the transducer. More specifically, an embodiment relates to an electromechanical transducer that is used as ultrasonic transducers and a method of producing the transducer.
2. Description of the Related Art
Electromechanical transducers such as capacitive micromachined ultrasonic transducers (CMUTs) produced by micromachining technology have been being researched as substitutes for piezoelectric transducers. These capacitive electromechanical transducers may receive and transmit ultrasonic waves with vibration of vibration films.
As a method of producing a CMUT, U.S. Patent Publication No. 2005/0177045 describes a method where a cavity is formed by etching of a sacrificial layer. In the method described in U.S. Patent Publication No. 2005/0177045, in order to prevent an upper electrode from being etched during the etching of the sacrificial layer, a second electrode is disposed between a first membrane and a second membrane, and the sacrificial layer is etched.
As in the method described in U.S. Patent Publication No. 2005/0177045, a CMUT is produced by sequentially stacking a lower electrode, an insulating film, an upper electrode, and a membrane on a substrate. In the case of forming a plurality of layers, the thicknesses of the layers tends to vary. If the thicknesses of layers are different among cells or elements, the frequency characteristics among the cells or the elements vary.